JP3525403B2 - Electrode materials and secondary batteries - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a battery electrode material. More specifically, it relates to a sulfide-based electrode material.

[0002]

2. Description of the Related Art In recent years, communication equipment and office automation equipment have become portable, and competition for weight reduction and miniaturization of these equipment has been promoted. Higher efficiency is also required for such various devices and secondary batteries used as power sources for electric vehicles and the like. In response to this demand, batteries using new electrode materials are being developed, but because of the relatively high energy density among them, electrode materials using sulfide compounds (hereinafter referred to as “sulfide electrode materials”) (US Patent No. 4833048 and the like) are attracting attention. This uses a sulfide compound having a triazine ring or a thiadiazole ring as an electrode material.

Here, the disulfide compound is R--S--S.
When represented as —R (R is an organic functional group), the disulfide bond (S—S bond) is cleaved by supplying two electrons by electrolytic reduction, and is bonded to a cation or a proton (M ⁺ ) in the electrolytic solution to give 2 ^{(R-S - · M +} ) becomes sulfide compound is represented by, at the time of electrolytic oxidation back to the original R-S-S-R, to release the 2 electrons. It is said that this secondary battery can be expected to have an energy density of 150 Wh / kg or more, which is equal to that of other ordinary secondary batteries. However, the inventors of the above-mentioned U.S. patents have been proposed by J. Electrochem. Soc. Vol. 136. No. 9, p.
From the content reported in 2575 (1989), the electron transfer rate of the electrode reaction of this sulfide-based secondary battery is extremely slow, and therefore it is difficult to extract a large current suitable for practical use near room temperature, and it is difficult to obtain a temperature of 60 ° C or more. A problem was pointed out that it was limited to use in the.

Then, as a technique for improving this sulfide-based secondary battery to cope with a large current, Japanese Patent Laid-Open No. 5-744 has been proposed.
As disclosed in Japanese Patent No. 59, etc., an electrode material has been proposed in which an organic compound having a thiadiazole ring and a disulfide group is combined with a conductive polymer such as polyaniline. However, in the secondary battery according to the conventional technique, although the current value can be expected to increase due to the increase in the reaction rate, the energy density cannot be improved, but rather has a drawback that it decreases.

[0005]

DISCLOSURE OF THE INVENTION The present invention, when applied to an electrode material of a secondary battery, can improve the energy density remarkably, and a sulfide-based electrode material having a remarkably high energy density. The purpose is to provide.

[0006]

In order to solve the above-mentioned problems, the organic electrode material of the present invention has a tetrazole ring-containing sulfite for a non-aqueous secondary battery as described in claim 1.
An electrode material for a positive electrode, which is 5,5'-dithiobis
(1-methyltetrazole), 5,5'-trithiobis
(1-methyltetrazole), 5,5'-tetrathiobi
Sus (1-methyltetrazole), 5,5'-dithiobis
(1-phenyltetrazole), 5,5'-trithiobi
Su (1-phenyltetrazole) and 5,5'-
Any of tetrathiobis (1-phenyltetrazole)
Sulfide for non-aqueous secondary battery characterized by being
It is an electrode material for a positive electrode . In addition, the non-aqueous secondary battery of the present invention
The pond has a tetrazole ring as described in claim 2.
Is a non-aqueous secondary battery that contains quality as a positive electrode active material.
And the substance having the tetrazole ring is 5,5′-dithio.
Bis (1-methyltetrazole), 5,5'-trithio
Bis (1-methyltetrazole), 5,5'-tetrati
Obis (1-methyltetrazole), 5,5'-dithio
Bis (1-phenyltetrazole), 5,5'-triti
Obis (1-phenyltetrazole) and 5,
Of 5'-tetrathiobis (1-phenyltetrazole)
It is a non-aqueous secondary battery characterized by being either
It

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the sulfide-based electrode material having a tetrazole ring means a compound in which a sulfur atom is directly bonded to the tetrazole ring, and a material containing these compounds. In addition, in a compound having a tetrazole ring, when a compound having two or more sulfur atoms per tetrazole ring is used, a multimer is formed. In this case, the energy density is improved.

Of these sulfide-based electrode materials having a tetrazole ring, those having a group represented by Chemical formula 1 or an ion represented by Chemical formula 2 for reasons such as high energy density and easy synthesis. Is desirable. In particular, a dimer (see Chemical Formula 3) is desirable because its capacity is not significantly reduced even when the number of charge / discharge cycles increases. In Chemical formula 3, when n is a polysulfide compound such as trisulfide having 1 or more and 5 or less,
It is preferable because the energy density becomes high.

[Chemical 3]

However, in the group represented by the chemical formula 1 and the ion represented by the chemical formula 2 or the substance represented by the chemical formula 3, R is a methyl group, an alkyl group such as an ethyl group, an amino group,
A carboxyl group, an alkylamino group, an amide group, a cyclic organic compound such as an aromatic compound, or a compound having hydrogen introduced may be used, but a group having an electron donating property such as a methyl group is preferable.

Since the above active material does not have conductivity, it is mixed with an electronic conductive material and an ionic conductive material to prepare a positive electrode. As the electron conductive material, carbon or titanium, metal powder such as nickel can be used, and as the ionic conductive material, a liquid electrolyte obtained by mixing an electrolyte salt such as perchlorate and a solvent such as propylene carbonate, Alternatively, a solid electrolyte such as polyethylene oxide in which an electrolyte salt is dissolved can be used.

Further, any of the above liquid electrolyte and solid polymer electrolyte can be used as an electrolyte of a battery.
On the other hand, as the negative electrode material, an alkali metal or a material into / from which an alkali metal is inserted / removed can be used.

[0012]

【Example】

[Example 1: Evaluation by cyclic voltammetry using 5,5'-dithiobis (1-methyltetrazole)] [Synthesis of 5,5'-dithiobis (1-methyltetrazole)] 30 ml of methanol under an argon atmosphere To 5
A solution of 10 mmol of 5-mercapto-1-methyltetrazole and 5 mmol of sodium methoxide dissolved in 30 ml of methanol was slowly added dropwise to dissolve 0.9 mmol of iodine, followed by stirring for 3 hours and then cooling to -60 ° C. The resulting precipitate was separated by filtration, dried under reduced pressure, and recrystallized three times with ethanol to give 5,5′-dithiobis (1-methyltetrazole).
Got

[2,2'-dithiobis (5-methyl-
Synthesis of 1,3,4-thiadiazole)] 2-mercapto-instead of 5-mercapto-1-methyltetrazole
The same procedure as in the synthesis of 5,5′-dithiobis (1-methyltetrazole) was performed except that 5-methyl-1,3,4-thiadiazole was used.

In addition, since the target substance is contained in the filtrate in addition to the filtered substance in the filtration step of each synthesis described above, the recovery and purification were performed separately, but the description thereof is omitted. Further, regarding these obtained products, F
It has been confirmed to be a target substance by an AB mass spectrometer and an infrared spectroscopic analyzer.

A battery was formed using 5,5'-dithiobis (1-methyltetrazole) and 2,2'-dithiobis (5-methyl-1,3,4-thiadiazole) obtained as described above. . Note that all the following work was performed under an argon gas flow in the glove box.

Two electrolytes were prepared by dissolving lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) as an electrolyte in 30 ml of γ-butyrolactone so as to have a concentration of 0.2 mmol / l. 5,5'-dithiobis (1-methyltetrazole)
And 2,2′-dithiobis (5-methyl-1,3,4-
5 mm of two disulfide compounds (thiadiazole)
Dissolved to a concentration of ol / l.

Using these two kinds of solutions, a battery was formed using glassy carbon as a sample electrode, a platinum wire as a counter electrode, and a silver-silver ion electrode as a reference electrode, respectively.
At this time, a battery having 5,5′-dithiobis (1-methyltetrazole) was used as Battery 1 (Example 1), 2,2′-dithiobis (5-methyl-1,3,4-thiadiazole).
The battery having the above was designated as Battery 2 (Comparative Example 2). Cyclic voltammograms of these batteries 1 and 2 were measured. The result is shown in FIG.

In FIG. 1, when comparing the cyclic voltammograms of the battery 1 and the battery 2, the deviations of the oxidation potential showing the peak of the oxidation current and the reduction potential showing the peak of the reduction current are almost the same, but the peak current values are Very different,
It can be seen that there is a big difference in the reaction rate. It is also understood that both of these peak potentials of the battery 1 according to the present invention are shifted in a noble direction as compared with the battery 2, and a higher voltage can be taken out.

Similarly, it was found from FIG. 1 that the amount of reducing electricity corresponding to the amount of discharging electricity of the battery 1 was 1.7 times that of the battery 2. This shows that 5,5′-dithiobis (1-methyltetrazole) has higher electrochemical activity than 2,2′-dithiobis (5-methyl-1,3,4-thiadiazole). . Further, the reduction potential at that time is shifted to the noble side as compared with Battery 2,
The amount of discharge energy (product of reduced electricity and potential difference) becomes larger.

Here, the molecular weight of 5,5'-dithiobis (1-methyltetrazole) is 2,2'-dithiobis (5
-Methyl-1,3,4-thiadiazole) is smaller than the molecular weight of (5,5'-dithiobis (1-methyltetrazole) as an active material, it is advantageous in the present invention. Conventional electrode material is 2,
It is clear that it is significantly superior to 2'-dithiobis (5-methyl-1,3,4-thiadiazole).

[Examples 2 to 7: Examination by coin type cell] The examination results by the coin type cell are shown below. In addition,
In these examinations, in the process where the inclusion of nitrogen, oxygen, moisture, etc. in the air should be avoided, work was carried out in an argon gas stream as needed. Further, as the solvent and the like, those obtained by dehydration, distillation and the like were used.

[Synthesis of Active Material] (Synthesis of 5,5′-dithiobis (1-methyltetrazole)) In a 1000 ml round-bottomed flask, 100 mmol of 5-mercapto-1-methyltetrazole was added to 450 m.
It was dissolved in 1 of methanol and cooled in a water bath. 20 ml of 34.5% hydrogen peroxide solution was slowly added dropwise to this solution. A few minutes after the dropping, the reaction generated heat and a precipitate was formed. The precipitate after the filtration was washed with methanol and then dried under reduced pressure to obtain 5,5′-dithiobis (1-methyltetrazole) (see Chemical formula 4: hereinafter referred to as “active material α”).

[0023]

[Chemical 4]

(Synthesis of 5,5'-trithiobis (1-methyltetrazole)) 5
-Mercapto-1-methyltetrazole 100 mmol
Was dissolved in 800 ml of diethyl ether. Next, 100 ml of a 1.25 mol / l sulfur dichloride / diethyl ether solution was slowly added dropwise thereto. The liquid gradually became cloudy and a precipitate was formed. After completion of dropping, the mixture was stirred for 1 hour, then cooled to -40 ° C and further precipitated. The filtered precipitate is washed with diethyl ether and then dried under reduced pressure,
5,5'-trithiobis (1-methyl-tetrazole)
(See Chemical formula 5: hereinafter referred to as “active material β”).

[0025]

[Chemical 5]

(Synthesis of 5,5'-tetrathiobis (1-methyltetrazole)) 5,5'-trithiobis (1-
Methyl-tetrazole), but with 1.
Instead of the 25 mol / l sulfur dichloride / diethyl ether solution, a 1.25 mol / l disulfur dichloride / diethyl ether solution was used ((5,5′-tetrathiobis (1-methyltetrazole) Hereinafter referred to as "active material γ").

[0027]

[Chemical 6]

(Synthesis of 5,5'-dithiobis (1-phenyltetrazole)) Similar to the synthesis of 5,5'-dithiobis (1-methyltetrazole) except that 5-mercapto-1-methyltetrazole is replaced by 5 -Mercapto-1-phenyltetrazole was used to obtain 5,5'-dithiobis (1-phenyltetrazole) (see Chemical formula 7: hereinafter referred to as "active material δ").

[0029]

[Chemical 7]

(Synthesis of 5,5'-trithiobis (1-phenyltetrazole)) 5,5'-trithiobis (1-
Methyltetrazole), except that 5-mercapto-1-phenyltetrazole is used instead of 5-mercapto-1-methyltetrazole to obtain 5,5′-trithiobis (1-phenyltetrazole) (see Chemical Formula 8: “Active material ε”) was obtained.

[0031]

[Chemical 8]

(Synthesis of 5,5'-tetrathiobis (1-phenyltetrazole)) Same as 5,5'-tetrathiobis (1-methyltetrazole) except that 5-mercapto-1-methyltetrazole is replaced by 5- 5,5 ′ with mercapto-1-phenyltetrazole
-Tetrathiobis (1-phenyltetrazole)
Reference: hereinafter referred to as “active material ζ”) was obtained.

[0033]

[Chemical 9]

(2,2'-dithiobis (5-methyl-
Synthesis of 1,3,4-thiadiazole) 2-mercapto-5-methyl-1,3,4-thiadiazole 150 mm
ol is dissolved in 450 ml of methanol and 39 m
1 of 34.5% hydrogen peroxide solution is slowly added dropwise, and the mixture is stirred at room temperature for 1 hour. After that, a precipitate was generated by reducing pressure and heating, filtering, washing with methanol, and then drying under reduced pressure to obtain a crude crystal. Recrystallize with ethanol,
5′-dithiobis (5-methyl-1,3,4-thiadiazole) (hereinafter referred to as “active material η”) was obtained.

(2,2'-trithiobis (5-methyl-
Synthesis of 1,3,4-thiadiazole) 2-mercapto-5-methyl-1,3,4-thiadiazole 100 mm
is dissolved in 200 ml of tetrahydrofuran, and 125 mmol of sulfur dichloride is slowly added dropwise thereto (a precipitate is formed by the addition). 5-1 at room temperature after dropping
Stir for 0 minutes. Then, after filtration and washing with tetrahydrofuran, the precipitate was dried under reduced pressure to obtain 5,5′-trithiobis (5-methyl-1,3,4-thiadiazole) (hereinafter referred to as “active material θ”).

(Synthesis of 2,2'-tetrathiobis (5-methyl-1,3,4-thiadiazole)) Similar to the synthesis of 2,2'-trithiobis (5-methyl-1,3,4-thiadiazole), However, 125 mmol of sulfur dichloride
Using 125 mmol of disulfur dichloride instead of 2,
2′-Tetrathiobis (5-methyl-1,3,4-thiadiazole (hereinafter referred to as “active material ι”) was obtained.

[Analysis of Active Material] The active materials α to ζ were analyzed. That is, CHNS analysis and O analysis (Perkin Elmer PE series II, CHNS / O analyzer), FAB-MS analysis, ¹ H-NMR and ¹³ C-
NMR spectrum analysis was performed. The molecular weight confirmed by CHNS analysis and 0 analysis result (mass ratio of carbon, hydrogen, nitrogen, sulfur, and oxygen in integer ratio based on nitrogen) and FAB-MS analysis are shown in Table 1, ¹ H-NMR and ¹³ C-
The results of the NMR spectrum analysis are shown in Table 2 for the active material α.
¹ H-NMR spectrum and ¹³ C-NMR spectra in FIGS. 2 and 3, respectively, showing the active material δ of ¹ H-NMR spectrum and ¹³ C-NMR spectra in FIGS. 4 and 5.

[0038]

[Table 1]

[0039]

[Table 2]

[Preparation of Positive Electrode] 33 parts by weight of each of the active materials α to ι, 18 parts by weight of lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) and 42 parts by weight of polyethylene oxide (molecular weight 2 million). , And 7 parts by weight of carbon black (Ketjenblack made by Lion) were respectively added, and a small amount of acetonitrile was added to this to facilitate mixing, and the mixture was stirred and mixed to obtain a slurry. The film was developed using a Teflon dish and then dried at 80 ° C for 24 hours.
0 μm (average), and these were punched out to a diameter of 15 mm to obtain a positive electrode.

[Preparation of Solid Electrolyte] Acrylonitrile-
Methyl acrylate copolymer 1.5g, and 1mol
Γ-butyrolactone solution of lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ) at a concentration of 1 / l, 6.0 m
l was mixed, spread on a petri dish, heated to 120 ° C., then gradually cooled, and punched to have a diameter of 1.5 mm. This also serves as a separator during battery assembly.

[Production of Cathode] A cathode was produced by punching out a lithium metal foil (thickness: 1.2 mm) to have a diameter of 15 mm. [Assembly of Coin-Type Cell] A coin-type cell whose cross section is shown in FIG. 6 using a positive electrode, a solid electrolyte and a cathode containing the above-mentioned nine types of active materials as active materials (9 types, Examples 2 to 7).
And two each of Comparative Examples 2-4) were produced. In the figure, reference character A is a negative electrode can, B is a negative electrode, C is a solid electrolyte (also serves as a separator), D is a positive electrode, E is a stainless steel collector,
F is a positive electrode can, and G is a gasket that separates the inside of these batteries from the outside air and prevents a short circuit between the negative electrode can and the positive electrode can.

[Evaluation of Coin Cell] The above active materials α to ι
The coin type cell having One of the two cells prepared for each active material was 0.2 m with respect to the positive electrode area.
A / cm ^2, it was carried out and the other with a current which is a current density of 0.4 mA / cm ^2. All charging / discharging is performed in a constant temperature air bath at 20 ° C., charging is performed at the above current density until the interelectrode voltage becomes 4.5 V, and discharging is performed at the above current density and the interelectrode voltage is 2.0.
It went to V. The evaluation was performed by repeating charging and discharging twice in advance and then charging and then discharging. 0.
The results at a current density of ² mA / cm ² are shown in Table 3, 0.4 m
Table 4 shows the results at a current density of A / cm ² .
The capacity density in these tables is the capacity per weight of the positive electrode, and the energy density is the value obtained by multiplying the average voltage during discharge by the capacity density. In addition, the utilization rate is 100 when the active material in the positive electrode is assumed to be involved in discharge.
It is a value showing the ratio of the actual amount of electricity when it is defined as%. Further, as FIG. 7, discharge curves (current density: current density: in the cells using the active materials α, δ, and η at the time of evaluation (the battery of Example 2, the battery of Example 5, and the battery of Comparative Example 2 respectively).
0.2 mA / cm ² ) is shown.

[0044]

[Table 3]

[0045]

[Table 4]

Comparing the average discharge voltages of the secondary batteries of Examples 2 to 4 and the secondary batteries of Comparative Examples 2 to 4 in Tables 3 and 4, the secondary batteries using the electrode material according to the present invention were compared. In this case, compared with a secondary battery using an electrode material having a thiadiazole ring, the voltage was increased by almost 300 mV, and the phenomenon observed by cyclic voltammetry in Example 1 and Comparative Example 1 was also exhibited in the button cell. It was confirmed. Thus, the average voltage is high, and since the capacity density is a little high, the secondary battery using the electrode material according to the present invention, compared with the secondary battery using the conventional electrode material having a tetrazole ring. It can be seen when it has a high energy density.

The secondary batteries shown in Examples 5 to 7 in which the active materials δ, ε and ζ having a phenyl group are used as electrode materials are respectively active materials α, β and γ having a methyl group. The utilization rate is high as compared with Examples 2 to 4 in which is used as the electrode material. Although the details are not clear, the conductivity as an electrode is improved by some interaction between the π-electron of the phenyl substituent and the π-electron of carbon, which is the current collector, so that the utilization rate may be improved. It is thought that there is.

Further, in the secondary battery using the electrode material according to the present invention, the discharge condition is 0.2 mA / cm ² to 0.
It can be seen that the positive electrode utilization rate does not decrease much even if it is increased to 4 mA / cm ² . As described above, it was confirmed that the secondary battery using the electrode material according to the present invention is excellent in that it can also be discharged with a large current.

[0049]

The tetrazole ring having four nitrogen atoms in the ring exhibits redox activity due to the interaction of the nitrogen atoms, like the organic electrode material having another aromatic heterocycle. Further, as compared with thiadiazole having sulfur in the molecule, the molecular weight of the heterocycle as the mother nucleus is about 17% smaller, and the mass of the sulfide compound as the positive electrode constituent can be reduced. Further, as is clear from the above Examples and Comparative Examples, the redox potential is a noble potential as compared with the case where thiadiazole is used, so a higher voltage can be taken out. As described above, the energy density of the secondary battery using the electrode material according to the present invention is significantly higher than that in the case of using the conventional electrode material. Furthermore, even if the discharge current becomes large because the reaction speed is fast,
It is an excellent one with little decrease in the positive electrode utilization rate.

[Brief description of drawings]

FIG. 1 is a cyclic voltammogram of a battery 1 which is an example (Example 1) of the present invention and a battery 2 which is a comparative example (Comparative Example 2).

FIG. 2 is a diagram showing a ¹ H-NMR spectrum of an active material α.

FIG. 3 is a diagram showing a ¹³ C-NMR spectrum of an active material α.

FIG. 4 is a diagram showing a ¹ H-NMR spectrum of an active material δ.

FIG. 5 is a diagram showing a ¹³ C-NMR spectrum of an active material δ.

FIG. 6 is a view showing a cross section of a coin-type cell manufactured in an example.

FIG. 7: Discharge curve in a cell using active materials α, δ and η
(Current density: 0.2 mA / cm ²) Is a figure which shows.

[Explanation of symbols]

A negative electrode can B negative electrode C Solid electrolyte (also separator) D positive electrode E current collector F positive electrode can G gasket

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-135767 (JP, A) JP-A-7-233057 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/00-4/62 H01M 10/40 CA (STN) JISST file (JOIS)

Claims (2)

(57) [Claims] 1. A non-aqueous secondary battery having a tetrazole ring.
A sulfide-based positive electrode material for
Thiobis (1-methyltetrazole), 5,5'-tri
Thiobis (1-methyltetrazole), 5,5'-teto
Lathiobis (1-methyltetrazole), 5,5'-di
Thiobis (1-phenyltetrazole), 5,5'-to
Lithiobis (1-phenyltetrazole), and
5,5'-tetrathiobis (1-phenyltetrazo
Non-aqueous secondary battery characterized in that
Electrode material for sulfide-based positive electrodes. 2. A positive electrode active material containing a substance having a tetrazole ring.
A non-aqueous secondary battery containing as a quality,
The substance having a polyol ring is 5,5′-dithiobis (1-methyl).
Rutetrazole), 5,5'-trithiobis (1-methyi)
Rutetrazole), 5,5'-tetrathiobis (1-me
Tyltetrazole), 5,5′-dithiobis (1-phen)
Nyltetrazole), 5,5′-trithiobis (1-phenyl)
Phenyltetrazole) and 5,5'-tetrathio
Must be either bis (1-phenyltetrazole)
And a non-aqueous secondary battery.